Chapter 7 - "The Slug Club" - In which Harry thinks Malfoy might be a Death Eater, everyone departs for King's Cross, and before getting on the train Harry tells Mr. Weasley his suspicions. On the train, Harry finds he is more famous than ever, but sits with Neville and Luna until Slughorn invites him to tea. After hours of boring conversation, Harry sneaks into the Slytherins' compartment, invisible, and listens to Malfoy brag about working with Voldemort, but when the train stops Malfoy freezes Harry and leaves him behind.

A Very Different Diagon Alley
Harry, Hermione, and Ron run into Draco and Narcissa Malfoy at [Madam Malkin's], and after a brief confrontation, the [Malfoys] leave the shop and Hermione quickly buys her robes.
Harry, Hermione, and Ron, along with Hagrid, meet back up with the Weasleys and head over to [Weasleys' Wizard Wheezes].
Weasleys' Wizard Wheezes
Harry and his friends find [Weasleys' Wizard Wheezes] - thanks to a [U-NO-POO] sign - and start to look around the shop.
Fred and George show Harry, Hermione, and Ron around [Weasleys' Wizard Wheezes].
Fred, under the guise of showing his siblings around [Weasleys' Wizard Wheezes], grills Ginny about her love life, while Ron tries to take stuff from the shop for free.
Following Draco in Knockturn Alley
Harry spots Draco Malfoy heading down [Diagon Alley] alone - and he, Ron, and Hermione slip under the Invisibility Cloak to give chase.
Harry, Ron, and Hermione listen in as Draco Malfoy buys something from Mr. Borgin in [Borgin and Burkes] - and threatens him besides.
Hermione charges into [Borgin and Burkes] to try to figure out what Malfoy had bought, though she is unsuccessful. The trio then returns to [Weasleys' Wizard Wheezes].
Harry, discussing Malfoy with Hermione and Ron, figures out that Malfoy is a Death Eater.